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Results for “Sex Determination Processes”

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At least 19 recordsLinked to original sources
PubMed1994

The sex determination process in maize.

Maize partitions the sexes into different flowers on the plant, a condition called monoecy, which facilitates outcrossing. Sex determination in maize is a complex process involving an interplay between genetic determinants, the environment, and hormones. Unisexuality of flowers is achieved by the process of selective arrest and abortion of the inappropriate organ primordia within a bisexual floral meristem. Floral organ abortion is associated with the degeneration of cells within an immature primordia. Masculinizing genes are required for gynoecial abortion, feminizing genes arrest stamen development, and both types also control secondary sexual traits involving morphological characteristics of floral tissues. Gibberellins, steroid-like plant hormones, appear to play a pivotal role in the stamen abortion process and the feminization of floral tissues.

Genes, Plant↗
PubMed1999

The primary sex determination signal of Caenorhabditis elegans.

An X chromosome counting process determines sex in Caenorhabditis elegans. The dose of X chromosomes is translated into sexual fate by a set of X-linked genes that together control the activity of the sex-determination and dosage-compensation switch gene, xol-1. The double dose of X elements in XX animals represses xol-1 expression, promoting the hermaphrodite fate, while the single dose of X elements in XO animals permits high xol-1 expression, promoting the male fate. Previous work has revealed at least four signal elements that repress xol-1 expression at two levels, transcriptional and post-transcriptional. The two molecularly characterized elements include an RNA binding protein and a nuclear hormone receptor homolog. Here we explore the roles of the two mechanisms of xol-1 repression and further investigate how the combined dose of X signal elements ensures correct, sex-specific expression of xol-1. By studying the effects of increases and decreases in X signal element dose on male and hermaphrodite fate, we demonstrate that signal elements repress xol-1 cumulatively, such that full repression of xol-1 in XX animals results from the combined effect of individual elements. Complete transformation from the hermaphrodite to the male fate requires a decrease in the dose of all four elements, from two copies to one. We show that both mechanisms of xol-1 repression are essential and act synergistically to keep xol-1 levels low in XX animals. However, increasing repression by one mechanism can compensate for loss of the other, demonstrating that each mechanism can exert significant xol-1 repression on its own. Finally, we present evidence suggesting that xol-1 activity can be set at intermediate levels in response to an intermediate X signal.

Animals↗
PubMed1995

The molecular genetics of Sry and its role in mammalian sex determination.

The process of sex determination, by which is meant the decision as to whether an embryo develops as a male or a female, is considered as a paradigm of how gene action can influence developmental fate. In mammals the decision is dependent on the action of the testis determining gene present on the Y chromosome, now known to be the gene Sry. Sry is expressed for only a brief period in the mouse embryo and must act to initiate rather than maintain the pathway of gene activity required for testis differentiation. It probably acts within cells of the supporting cell lineage to direct their differentiation into Sertoli cells, rather than the granulosa cells characteristic of the ovary. Other lineages in the gonad then follow the male pathway. The nature of the Sry transcript in the genital ridge of mice has been determined and compared with that from the human gene which is dramatically different. The expression of Sry has been carefully examined during the critical stages of genital ridge development and compared to the expression of a number of other genes involved in gonadal development and male development such as that for anti-Mullerian hormone. This has defined the period in which Sry must act to between 11 and 11.5 days post coitum. The expression of Sry has also been examined in cases of sex reversal in the mouse. There is a dependence on level of expression and extent of testicular differentiation that suggests thresholds for both the amount of SRY per cell and the number of cells expressing the gene. The SRY protein interacts with DNA through an HMG box type of DNA binding domain, however at present no definite target genes have been found. Progress on strategies to find such genes is discussed.

Animals↗
PubMedDate not supplied

Sex determination: the amphibian models.

We review and discuss current knowledge about sex determination in amphibians. The astonishing wide variety of mechanisms of genotypic sex determination is presented and discussed in an evolutionary context. We recall the natural occurrence of transitory juvenile hermaphroditism in some species. Our present knowledge of the mechanisms of sex determination in amphibians is compared to that in mammals. The influence of epigenetic factors, and especially temperature is highlighted. In amphibians, the influence of temperature on sexual differentiation, that can prevail over genotypic sex determination, remains poorly considered in publications. We suggest that studies on genetic and epigenetic factors of gonadal sex differentiation in amphibians could provide substantial information on the evolutionary process of sex determination mechanisms in current living vertebrates.

Amphibians↗
PubMed2003

Sperm pre-incubation prior to insemination affects the sex ratio of bovine embryos produced in vitro.

The objective of the present study was to determine whether sperm incubation prior to oocyte insemination in vitro affects the sex ratio of resulting blastocyst. Cumulus-oocyte-complexes (COCs) collected from slaughterhouse ovaries were matured in vitro and inseminated with frozen-thawed semen of three proven artificial insemination (AI) bulls pre-incubated in vitro in Sperm-Talp for 6 and 24 h. On day-9 blastocysts were collected and processed for sex determination. More than 80% of blastocyst were successfully sexed. There were no significant differences in cleavage and blastocyst rates using sperm pre-incubated for 6 h as compared with the 0-h pre-incubation control group. The cleavage and blastocyst rates were significantly lower in the 24-h pre-incubation group. The male to female ratio, when compared with the theoretical 1 : 1, differed significantly in favour of females among hatched (viable) blastocysts derived from sperm pre-incubated for 24 h prior to insemination as well as among all blastocytsts in the 6-h group. Moreover, when the sperm treatment was considered, the sex ratio was affected only among hatched blastocysts in 24-h pre-incubation group. It was concluded that prolonged sperm pre-incubation influences the rate of development and the sex ratio among hatched blastocysts.

Animals↗
PubMed2004

Developmental sculpting of social phenotype and plasticity.

Early developmental variables engender behavioral and neural variation, especially in species in which embryonic environment determines gonadal sex. In the leopard gecko, Eublepharis macularius, the incubation temperature of the egg (IncT) determines gonadal sex. Moreover, IncT affects the sexual differentiation of the individual and, consequently, within-sex variation. Individuals hatched from eggs incubated at an IncT that produces predominantly males are more masculinized than same-sex counterparts from IncTs that produce predominantly females. Here we review how gonadal sex and IncT interact to affect behavioral, endocrinological, and neural phenotype in the leopard gecko and influence phenotypic plasticity following hormone administration or social experience. We discuss the hormonal dependence of sex- and IncT-dependent behavioral and neural morphological and metabolic differences and highlight the parallels between IncT effects in geckos and intrauterine position effects in rodents. We argue that the leopard gecko is an important model of how the process of sex determination can affect sexual differentiation and of selection forces underlying the evolution of sex ratios.

Animals↗
PubMed2004

Cloning and developmental expression of the cytochrome P450 aromatase gene (CYP19) in the European eel (Anguilla anguilla).

To characterize the involvement of the aromatase gene during the process of sex determination in the European eel (Anguilla anguilla), the expression of its gonadal form was determined during various developmental stages. The cloned cDNA from the European eel gonad (EeCYP19) contains an open reading frame of 1539 bp, encoding a deduced protein of 513 residues. The predicted amino acid sequence shows 97% identity with that of the Japanese eel, and 59-69% of identity with those of the CYP19 gonadal and brain forms of other teleost fish. Two potential initiation sites (ATG) were found downstream of the first ATG codon. A fluorescent-based method of real-time PCR was developed to quantify EeCYP19 expression. The expression levels of EeCYP19 in the gonads of adult males were approximately 12- and 30-fold lower than the levels in adult females and juvenile eels previously treated with E2, respectively. Expression of aromatase was found only in a single specimen in the control group. In contrast, no difference was found among sexes in the aromatase expression in the brain. Treatment with aromatase inhibitor (AI) of juvenile eel resulted in the total loss of aromatase expression in the gonads and brains. The results of this work revealed that AI treatment not only reduces the synthesis of estradiol, but reduces the expression levels of EeCYP19 as well. No evidence for the presence of a distinct extra-gonadal (brain) form of aromatase in the European eel could be provided.

Amino Acid Sequence↗